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Home arrow Archives   The American Surveyor     

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Written by Letters to the Editor   
Saturday, 23 February 2013

A 53Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

Zoned Out
Wendy, Great article. I read it, without realizing that you are the author, by clicking on the URL provided this morning by the American Surveyor newsletter. Only when I got to the bottom of the article, did I find that it is you who had, once again, stimulated my interest.

I am happy to admit that I am very much pro when it comes to zoning and its related legislation "the official plan--mainly because of the consultative process that is required to put any of these items in place or to amend them.

Our group, the Surveyor General Branch, deals with land on First Nation Reserves, where planning seems to be an after thought or totally non-existent. I did not realize that there are major U.S. cities where zoning is not part of the legislation. Thanks for enlightening us.
Murray J. LeGris, O.L.S., C.L.S., O.L.I.P.
Senior Surveyor, Ontario Regional Office
Natural Resources Canada


Lathrop Responds
Thank you for writing--it's nice to know that the topics I choose interest others as well, and I also appreciate learning from letters received in response. I am not sure that planning is often part of the development process on reserved lands here in the US, either, but I would defer to others with more direct experience beyond my mere reading of a smattering of articles. --WL

Measurement is Dead, Long Live Measurement
I enjoyed Michael Pallamary's thought provoking article "Measurement is Dead, Long Live Measurement." [Editor's note: the article can be found at http://www.amerisurv.com/content/view/10759/153/]

That said, I have an alternate point of view regarding the status of measurement. While I agree with Mr. Pallamary in principle, in my opinion some of his statements are too generalized and work around the edges of the problem without dealing directly with the problem itself.

Well over twenty-years ago, the center of gravity began to shift in measurement technology from the mechanical act of making measurements to measurement analysis. One can cite the advent of electronic surveying systems and desktop least-squares as the shape of things to come. In my opinion, what distinguishes the technician from the professional is the professional's ability to analyze measurements, rather than purely making observations (measurements).

Like many, I can cite several instances that I have witnessed over the years of misapplied technology ranging from bad RTK calibrations, the improper use of least-squares/coordinate transformations, or using the wrong tool for the task. From my perspective, some have become too comfortable with the results from some of the more modern automated measurement systems.

Anecdotally, I can share one project that illustrates my point. Two years ago, I was involved in a vertical control survey in a relatively steep portion of Los Angeles County in support of a project along one of our transportation routes. We were required to re-run third-order leveling originally performed by a surveyor under contract to the State that was completed several years before. The leveling route contains a difference in elevation of over 1300 feet (400 m) over a distance of roughly 15 miles (25 km).

At the time, the original surveyor's leveling network misclosed when compared to the published NGS benchmarks by upwards of 0.6' (18 cm); his solution was to constrain both ends of his leveling network and simply "adjust out" any remaining misclosure. What we subsequently discovered was that the fiberglass leveling rods used by the original surveyor were systematically too short. After the proper scale correction was applied to the measurements, all the original surveyor's leveling observations agreed with the NAVD 88 benchmarks published by NGS to within 0.04' (12 mm), a very different result from the original 0.6' misclosure. Our results were also confirmed independently using GNSS methods completed at the same time as our re-leveling. Briefly, this became a control surveying version of "my chain versus the original surveyor's chain", or better put "the original surveyor's leveling rods versus NGS' leveling rods." Systematic scale errors in distance or height are identical regardless whether one analyzes geodetic leveling (correcting rod scale error) or boundary surveying (correcting a chain using proration).

It was a simple solution, but one that escaped the original surveyor because (my suspicion) his digital level and least squares told him so. Perhaps the original surveyor thought that since he was using state-of-the art equipment, his results could not possibly be wrong. The cold hard reality is that the original surveyor never went beyond what the black box told him to investigate why his leveling survey had such a high misclosure relative to stable first-order NAVD 88 benchmarks published by NGS. His measurement analysis was flawed but his measurements were correct because the scale error could have been corrected prior to using a least-squares solution. (Reference: Caltrans District 7 Survey Request SR 10-211).
Jay Satalich, PS
California Department of Transportation
District 7

A 53Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

 
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